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Selectivity of fragmentation and rearrangements of ether radical cations in the liquid-phase radiolysisстатья
Информация о цитировании статьи получена из
Web of Science,
Scopus
Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
- Авторы: Belevskii V.N., Belopushkin S.I., Baranova I.A., Tyurin D.A.
- Журнал: High Energy Chemistry
- Том: 33
- Номер: 6
- Год издания: 1999
- Издательство: Pleiades Publishing, Ltd
- Местоположение издательства: Road Town, United Kingdom
- Первая страница: 379
- Последняя страница: 389
- Аннотация: The formation of radical products in the radiolysis of a series of ethers [Me2O, Et2O, (CH3CD2)(2)O, iso-Pr2O, n-Bu2O, CH3OCH2OCH3, and CH3OCH2CH2OCH3] was studied using tert-nitrosobutane and 2,4,6-tri-tert-butylnitrosobenzene as spin traps. It was shown that only for methyl ethers (such as Me2O and CH3OCH2OCH3) the fragmentation resulted mainly in formation of both (CH3)-C-. and CH3O. radicals with comparable yields (in addition, the (CH2OCH3)-C-. type radicals were formed). In the cases of diethyl ether, C-3, and C-4 ethers, the main fragmentation products were found to be the RO. radicals; meanwhile, the adducts with distonic radical cations resulting from intramolecular rearrangement were observed instead of adducts with alkyl radicals. The reasons for selective fragmentation may be concerned with considerably lower ionization potentials for RCH2CH2. and (CH3CHCH3)-C-. type radicals (in comparison with (CH3)-C-. and RO. radicals), which result in predominant formation of (CH3)-C-. and RO. radicals. The distonic radical cations are considerably more stable than the corresponding classic isomers from the energetic point of view. The ab initio calculations also revealed a substantial decrease in the activation energy for intramolecular H-atom transfer within the series Me2O, Et2O, Pr2O, n-Bu2O, n-BuOMe (down to ca. 16.7 kJ/mole). For this reason, the rearrangement of this kind is possible even at 77 K in freonic matrices in the cases of Pr2O and n-Bu2O radical cations. In the case of radiolysis of neat ethers, the primary radical cations are formed with considerable excess energy, which facilitates fragmentation and rearrangements even for Me2O and Et2O radical cations, in spite of rather high barriers. The data on fragmentation of ether radical cations in liquid phase are in agreement with the results obtained in krypton and argon matrices. The radical cations resulting from indirect ionization in freonic matrices do not possess excess energy, and, typically, the fragmentation products are not formed.
- Добавил в систему: Тюрин Даниил Александрович